Global Hydrology


Numerical climate modelling

Numerical climatic models are used for deeper understanding of the climate-system, and for prediction of the future climate and water resources. They are composed of physical-based equations,and meteorological components (such as temperature, wind velocity, and the volume of evapotranspiration and so on...) are obtained by integration of these equations from certain initial conditions. A climatic model is composed of four sub-models; Atmospheric General Circulation Models, Oceanic General Circulation Models, and Land Surface Models. To understand the whole climate-system, understanding interactioms between these each sub-systems is important. From that point of view, researches about interaction especially between the atmosphere and the land have been performed in the laboratory.

Application of SiB2 to a Tropical Paddy Field and Inclusion of Water Body

SiB2, one of the newest Land Surface Models was applied to observational data at a tropical paddy field. Under the case of small Leaf Area Index (LAI), latent heat flux (lE) was underestimated.(fig.1) Because under smaller LAI, evapotranspiration mainly occurs at land or water surface but not at the top of the canopy. Further, surface water is easily lost and evaporation decreases because of low capacity of surface water in SiB2.
fig.1
In order to make up for these defects, SiB2-Pad in which water body is taken into account was developped and applied. As a result, the simulation of the latentheat flux was improved significantly.(fig.2) Ground surface temperature was estimated fairly well, but during nighttime, water temperature was underestimated. Canopy temperature was also lower than observation during nighttime. As a result, slight underestimation of lE in the morning was not improved. Additionally, canopy temperature was sometimes overestimated in the simulations, that caused underestimation of lE. (fig.3) In order to avoid the underestimation, it was necessary to adjust a parameter representing dependency of stomatal-conductance on leaf temperature.

fig.2
fig.3